Amblyopia is the most frequent cause of visual loss in childhood (Sachsenweger, 1968), and thus represents a significant clinical problem. Recent experiments suggest that amblyopia involves abnormalities of pattern discrimination rather than simple detection. Moreover, amblyopes of different etiologies show different patterns of loss. The development of new psychophysical techniques for studying fine spatial and temporal discriminations and new quantitative methods for analyzing the processes involved in such discriminations may make it possible to thoroughly characterize the visual system of amblyopes. The use of perturbations (eg. noise, adaptation, etc) to highlight cues or render them ineffective will provide insight into specific mechanisms involved. The proposed research will capitalize on these methodologies to characterize: 1. Spatial position, phase, shape, size, and motion discrimination 2. Temporal discrimination and spatio temporal interactions 3. Binocular interactions and 4. High order perceptual process in humans with naturally occurring amblyopia. In most of the experiments, the performance of the amblyopic eye will be compared to that of another degraded visual system, the normal periphery. Quantitative modelling of both amblyopic and peripheral vision will be undertaken. In addition, the development and implementation of psychophysical tests for children which are simple, rapid and sensitive to the losses of amblyopia is a high priority of this application. The development of a battery of such tests will be useful in clinical evaluation of amblyopes and in monitoring developmental changes and the effects of treatment.